shopify header html work

I require an experienced Shopify developer who can insert an image banner into my website's header. I'd like the banner to show up on mobile devices only informing the customer to rotate their phone. I have the banner made, in two size widths already, and will provide the shopify image link source required. Once complete, I wish to for the developer to show me where the code is, so I can change the img src banner on the fly myself. Upon rotating the phone, the banner should disappear as the phone would then show the desktop version of the header.

Two images attached, shows preview of current mobile header, and one with the desired outcome.

Also attached are the two banners I made in house.